In recent years, along with the development and the spread of computers, various kinds of information are converted into digital data. As a device for storing such digital data, a storage device such as a magnetic disk has been known. However, in preparation for unexpected circumstances such as a failure of the storage device, the data must be replicated and stored in another storage device.
As data replication methods between storage devices, the following methods have been known. One method is to replicate data via a network. In this method, a data transfer path is established between the devices using a protocol such as TCP/IP (Transmission Control Protocol/Internet Protocol) or FC (Fibre Channel) protocol, and data is transferred from the replication source to the replication destination through the path. Patent Document 1 discloses an exemplary system thereof.
Another method is to temporarily move a storage unit such as a HDD (Hard Disk Drive) governed by a transfer destination storage device so as to directly connect it with the transfer source. It is also possible to directly connect them constantly.    Patent Document 1: JP 2003-141054 A